Abstract

Adult memory T cell repertoires are populated by clonotypes that correspond to an individual's history of antigen exposures. The population density of clonotypes in the memory repertoire is important in light of the greatly reduced production of naïve T cells by the involuted thymus and the continuing need to respond to novel pathogens. We measure clonotypic density by comparing the recall response to the influenza-derived, HLA-A2 restricted, M158-66 peptide, with those to peptides substituted at positions 63 and 65 (TCR contact residues). The PBMC were from individuals who show a complex repertoire in recall response to the M158-66 peptide. All samples were obtained under an IRB approved protocol. Peptide-specific responses were identified by CDR3 spectratype analysis, and the clonotypes identified by sequencing the CDR3. As the substitutions became more pronounced, the M158-66 repertoire was lost and new responding clonotypes were revealed. However, the number of new clonotypes identified was lower than observed for M158-66. Structurally similar substitutions revealed a limited cross-reactivity in M158-66 repertoire. These data indicate that the adult repertoire is populated by T cells that can recognize structurally related epitopes. However, these T cells are sparsely distributed for the peptide:MHC structures generated by our substitutions.